"Judges are not moral or intellectual giants, prophets, oracles, mouthpieces, or calculating machines. They are all-too-human workers," Richard Posner states in the introduction of How Judges Think (2009, p. 7). Yet all too often judges are put on a pedestal of rationality, and as a result, we lose the opportunity to discover and understand what human factors affect judicial decisions. Even if one accepts the positivist position and holds that the law is as it is written, distinct and separate from entities such as morality, the fact remains that the law is written, interpreted and applied by human hands and human minds very much affected by morals and emotions. The consequence is that judges and legislators, whether they know it or not, will draw upon their unconscious reservoirs of experience, social norms, morals, emotions and urges when making their decisions.
In this article we will examine how biological urges can be recognized in juridical verdicts. We hypothesize that biological mechanisms will become most clear in cases that concern reproduction and survival, as these are the ultimate aims of human genetics and it is likely that their importance will stimulate more emotional and unconscious reactions in the presiding judges, as well as more reliance on social norms that are predicated on biological mechanisms. We will therefore turn to an examination of the biological influences on judges and the law in two cases: R v Brown  1 AC 212 and R v The Queen (1981) 28 SASR 321. The first case concerns homosexuality and sadomasochism. The second case concerns a murder, which took place against the background of a history of serious domestic violence and sexual abuse. But first let us elaborate upon some aspects of biological law theory that are important to analyze these cases from a biological perspective.